1. Field
Embodiments of the invention relate to the field of communication, and more specifically, to echo cancellation.
2. Background
Acoustic echo is an inherent problem in the design of speech processing equipment such as telephone network and wireless handsets. Echo cancellation is a technique to reduce the amount of echo in the voice transmission by estimating the echo picked up on the microphone or line on the transmitting side and subtracts it from the ear piece or hands-free speaker on the receiver side. Since the exact model of the environment is not known and time-varying, adaptive techniques are typically used to estimate the echo.
There are two non-trivial real-world problems in echo cancellation: double-talk and changes in impulse response due to loudspeaker enclosure microphone (LEM) changes. Double-talk is caused by the simultaneous generation of speech signals from both the far-end and near-end ports of an electronic duplexer for a four-wire communication system. LEM changes are caused by various local changes such as movements of speaker, environmental noise, and temperature variations. These two problems require opposite behavior on the part of the echo canceller. Double-talk requires that the adaptive weights to be held unchanged, i.e., no adaptation whereas LEM changes require quick adaptation. In addition, when the channel impulse responses are sparse, the computations may be inefficient and may not be accurate.